Incorporating Rainfall-Runoff Events into Nitrate-Nitrogen and Phosphorus Load Assessments for Small Tile-Drained Catchments

Abstract

Rainfall-runoff events significantly influence water runoff and the loss of pollutants from tile-drained agricultural land. We monitored ten small (4 to 38 ha) tile-drained catchments in Czechia for three to five years (2012 to 2016). The discharge was measured continuously; a regular 14-day scheme of water quality monitoring was accompanied with event sampling provided by automatic samplers in 20 to 120 min intervals. A new semi-automated algorithm was developed for the identification of runoff events (RE) based on discharge and water temperature changes. We then quantified the share of RE on the total runoff and the N and P losses, and we compared six methods for nutrient load estimation on an annual and monthly basis. The results showed considerable differences among the monitored sites, seasons, and applied methods. The share of RE on N loads was on average 5% to 30% of the total annual load, whereas for P (dissolved and total), the share of RE was on average 10% to 80% on the total annual load. The most precise method for nutrient load estimation included the RE. The methods based on point monitoring of the discharge and water quality underestimated the loads of N by 10% to 20% and of P by 30% to 80%. The acquired findings are crucial for the improvement of nutrient load assessment in tile-drained catchments, as well as for the design of various mitigation measures on tile-drained agricultural land.

Water scarcity: regional analyses in the Czech Republic from 2014 to 2018

“…The dynamics of drainage runoff and consequently changes of pollutant concentrations and loads are often driven by rainfall-runoff events. During these events, drainage runoff could consist of a large portion of event water, which rapidly infiltrates through polluted topsoil by preferential pathways, and bring this pollution into drainage water (Zajíček et al, 2016;Fučík et al, 2017). Recently, with changes in precipitation distribution during the season, rainfall-runoff events have become an important component of the total runoff.…”

Long-Term Water Balance of Selected Field Crops in Different Agricultural Regions of the Czech Republic Using Fao-56 and Soil Hydrological Approaches

“…Generally, it can be stated that one-function drainage systems (free drainage), besides having the potential to reduce surface runoff and associated soil erosion, also decrease shallow GWL and drain subsurface water from the landscape, even when it is not necessary. The presence of drainage systems generally also deteriorates the quality of related waters, as they carry away dissolved nutrients and other pollutants from the soil by subsurface runoff [54,55].…”

Methods for Sample Collection, Storage, and Analysis of Freshwater Phosphorus

“…Furthermore, a rain gauge and flow meter should also be installed at the sampling site to record the rainfall intensity and runoff volume, respectively. Since it is difficult to collect frequent grab samples, particularly during continuous flows, studies have found this method insufficient to obtain time-weighted average concentrations [57,58]. Automated samplers can ease these drawbacks by taking continuous composite samples with off-site recording of rainfall and runoff flow as well as the date and time of sample collection.…”